U.S. patent application number 15/155490 was filed with the patent office on 2016-11-17 for method and system for non-persistent communication.
The applicant listed for this patent is Raytheon Company. Invention is credited to Thomas Borton, Gary M. Graceffo, Andrew Kowalevicz, Michael C. Reese.
Application Number | 20160336977 15/155490 |
Document ID | / |
Family ID | 54356001 |
Filed Date | 2016-11-17 |
United States Patent
Application |
20160336977 |
Kind Code |
A1 |
Kowalevicz; Andrew ; et
al. |
November 17, 2016 |
METHOD AND SYSTEM FOR NON-PERSISTENT COMMUNICATION
Abstract
A method for carrying data on a live host signal, comprising the
steps of: varying timing in a host signal in response to data to be
encoded, wherein variations in timing are smaller than a sampling
period for detection and capture of the digital signal receiving
the live host signal; sensing pulse timing variations in the
received live host signal by comparison to a reference signal; and
determining information in the sensed timing variations.
Inventors: |
Kowalevicz; Andrew;
(Arlington, VA) ; Borton; Thomas; (Rockville,
MD) ; Reese; Michael C.; (Fairfax, VA) ;
Graceffo; Gary M.; (Burke, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Raytheon Company |
Waltham |
MA |
US |
|
|
Family ID: |
54356001 |
Appl. No.: |
15/155490 |
Filed: |
May 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14704916 |
May 5, 2015 |
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15155490 |
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61988418 |
May 5, 2014 |
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61988423 |
May 5, 2014 |
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61988416 |
May 5, 2014 |
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61988409 |
May 5, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 43/087 20130101;
G09C 1/00 20130101; H04L 25/4902 20130101; H04B 1/0475 20130101;
H04L 7/065 20130101; H04L 43/0864 20130101; H04L 9/16 20130101;
H04L 9/08 20130101; G06F 1/12 20130101; H04L 7/042 20130101 |
International
Class: |
H04B 1/04 20060101
H04B001/04; H04L 25/49 20060101 H04L025/49; H04L 7/04 20060101
H04L007/04 |
Claims
1.-8. (canceled)
9. A method for encoding data in a carrier signal comprising:
encoding a data signal in timing jitter of the carrier signal
having timing jitter of a given level; and transmitting the encoded
carrier signal.
10. The method of claim 9 wherein encoding the data signal in the
timing jitter of the carrier signal comprises varying the timing in
the carrier signal in response to the data signal to be encoded,
wherein variations in the timing are smaller than a sampling period
for detection and capture of the encoded carrier signal.
11. The method of claim 10 wherein the carrier signal is a
regenerated version of an existing signal; and the regenerated
version has at least one frequency component with lower phase noise
than the existing signal from which it was created; and wherein the
carrier signal was regenerated by using a frequency reference from
a high stability oscillator that has a level of stability that is
greater than the level of stability of the existing signal.
12. The method of claim 9 wherein the data signal is configured to
be recovered from the timing jitter of the encoded carrier signal
by sensing variations in the timing of the encoded carrier signal
by comparison of the modulated carrier signal to a first reference
signal that has a level of stability that is greater than the level
of stability of the encoded carrier signal.
13. The method of claim 9, wherein the data signal represents
covert data, the carrier signal is a digital signal and the timing
jitter comprises variations in pulse timing.
14. The method of claim 13, wherein the pulse timing variations
comprise variations of one of a leading edge of digital pulses, a
trailing edge of digital pulses or pulse width of digital
pulses.
15. The method of claim 13, wherein the digital pulses comprise
marks and spaces and wherein the pulse timing variations comprise
variations in time position of the marks and spaces.
16. The method of claim 9, wherein the carrier signal is a periodic
waveform or a non-periodic waveform, and the timing variations are
performed by modulating the phase of at least one frequency of the
carrier signal.
17. The method of claim 9 wherein the carrier signal is a periodic
waveform or a non-periodic waveform, and the timing variations
comprise variations of one of a particular bit represented by a
waveform or of a plurality of bits represented by the waveform.
18. The method of claim 17 wherein the plurality of bits are
consecutive or non-consecutive.
19. A transmitter for surreptitious communication of data
comprising: a carrier signal source and a data signal source; a
high stability oscillator configured as a frequency reference to
generate the carrier signal from the carrier signal source with at
least one frequency that has a level of stability that is greater
than the level of stability of a receiver to which the
communication is intended to be surreptitious; and a modulator
coupled to the high stability oscillator and to the data signal
source to modulate the carrier signal with the data signal.
20. The transmitter of claims 19 wherein the data signal is encoded
onto the carrier either by modulating the high stability
oscillator, wherein the high stability oscillator generates a
frequency reference for carrier signal generation, or by modulating
the carrier signal after the carrier signal is generated by an
unmodulated high stability oscillator.
21. The transmitter of claim 19 wherein the carrier signal is a
frequency tone that has a level of stability that is greater than
the level of stability of the receiver to which the communication
is intended to be surreptitious.
22. The transmitter of claim 19 wherein the carrier signal is a
periodic or non-periodic waveform that has a level of stability
that is greater than the level of stability of the receiver to
which the communication is intended to be surreptitious.
23. The transmitter of claim 19 wherein the data signal is
configured to be decoded from the timing jitter of the encoded
carrier signal by sensing variations in the timing of the encoded
carrier signal by comparison of the modulated carrier signal to a
first reference signal that has a level of stability that is
greater than the level of stability of the encoded carrier
signal.
24. The transmitter of claim 19 wherein variations in the timing
are smaller than a sampling period for detection and capture of the
encoded carrier signal.
25. The transmitter of claim 19 wherein the encoder is configured
to encode the carrier signal by modulating the phase of at least
one of a plurality of frequencies of the carrier signal.
26. A receiver comprising: a carrier signal receiver configured to
receive an encoded carrier signal, the carrier signal being encoded
with a data signal in the timing jitter of the carrier; a high
stability oscillator configured to generate a first reference
signal that has a level of stability that is greater than the level
of stability of the received encoded carrier signal; and a
demodulator coupled to the high stability oscillator and to the
carrier receiver to demodulate the encoded carrier signal with the
first reference signal to produce a demodulated data signal.
27. The receiver of claim 26 wherein the first reference signal
comprises the carrier signal without the encoded data signal in the
timing jitter of the carrier signal, and wherein the data signal is
recovered by comparison of the encoded carrier signal to the
un-encoded carrier signal.
28. The receiver of claim 27 wherein recovery of the data signal
comprises detecting timing variations in the encoded carrier
signal.
29. The receiver of claim 26 wherein the first reference signal is
a frequency tone that has a level of stability that is greater than
the level of stability of the encoded carrier signal.
30. The receiver of claim 26 wherein the first reference signal is
a regeneration of the un-encoded carrier signal that has a level of
stability that is greater than the level of stability of the
encoded carrier signal.
31. The receiver of claim 26 wherein the data signal is decoded
from the timing jitter of the encoded carrier signal by sensing
variations in the timing of the encoded carrier signal by
comparison to the first reference signal that has a level of
stability that is greater than the level of stability of encoded
carrier signal.
32. The receiver of claim 26 wherein variations in the timing are
smaller than a sampling period for detection and capture of the
encoded carrier signal.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims the benefit
of priority to U.S. application Ser. No. 14/704,916, filed May 5,
2015, which claims the benefit of priority to U.S. Provisional
Patent Application Ser. No. 61/988,409, filed May 5, 2014, U.S.
Provisional Patent Application Ser. No. 61,988,416, filed May 5,
2014, U.S. Provisional Patent Application Ser. No. 61,988,423,
filed May 5, 2014, and U.S. Provisional Patent Application Ser. No.
61/988,418, filed May 5, 2014, the benefit of priority of each of
which is claimed hereby, and each of which are incorporated herein
by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to communication
devices, and in particular to such devices which communicate secure
information.
BACKGROUND OF THE INVENTION
[0003] Often times, when U.S. Diplomats are working outside the
continental United States (OCONUS), communications are closely
monitored by the visited country. The monitoring is done to
identify transmissions that are considered harmful to local
governments. When United States personal are operating in these
countries, they need to send their information back to the US using
encryption to protect their mission. There are, of course, other
instances where securely transmitted communications are very
useful. The sending of encrypted messages either over-the-air or
over a terrestrial link can bring undesired attention to the
sender, which could have damaging consequences. Therefore it is
useful to have a method for sending secure communications that do
not appear to be secure.
SUMMARY OF THE INVENTION
[0004] One embodiment of the present invention provides a method
for carrying data on a live host signal, comprising the steps of:
varying timing in a host signal in response to data to be encoded,
wherein variations in timing are smaller than a sampling period for
detection and capture of the digital signal; receiving the live
host signal; sensing timing variations in the received live host
signal by comparison to a reference signal; and determining
information in the sensed timing variations.
[0005] The variations in timing may be less than 1 picosecond. The
host signal may be a digital signal and the timing variations may
be pulse timing variations. The variations in pulse timing include
variation of a leading edge and a trailing edge of digital pulses.
The variations in pulse timing may include variation in pulse
width.
[0006] The reference signal is a frequency reference having a
stability that is better than the level of timing variations of the
host signal; and the timing variations of the host signal may be
smaller than the a sampling period for detection and capture of the
digital signal. The reference signal may have a known variation to
which the data to be encoded is added. The host signal may be an
analog signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The present invention is illustratively shown and described
in reference to the accompanying drawings, in which:
[0008] FIG. 1 is a diagram of a nominal waveform demonstrating
timing jitter.
[0009] FIG. 2 is a diagram of a waveform demonstrating the
difference between accuracy and precision.
[0010] FIG. 3 is a graph of jitter probability.
[0011] FIG. 4 is a block diagram of a data transmission system
according to the present invention.
[0012] FIG. 5 is a representational graph of timing variations used
in a covert communications channel in accordance with one
embodiment of the present invention.
[0013] FIGS. 6A and 6B are diagrams of waveforms associated with an
embodiment of the present invention.
[0014] FIG. 7 is a block diagram of a circuit constructed in
accordance with one embodiment of the present invention.
[0015] FIG. 8 is a graphic depiction of the application of one
embodiment of the present invention.
DETAILED DESCRIPTION
[0016] The present application presents a method and system for
hiding information in a host data stream, using by way of example,
Gaussian Clock Dither Modulation (GCDM) with a high stability
oscillator (HSO). A host (overt) communications channel is
transmitted in the open using the oscillator as a frequency
reference. The covert communication is applied to the host signal
by modulating the timing on the reference signal of the transmitter
to represent the covert (hidden) communication. While the timing
variation representing the covert communication is deterministic,
it is implemented such that it appears Gaussian in nature and
remains within the normal operational levels of timing jitter for a
less stable frequency standard of approximately 1 s-1.0 s of ps.
The variation introduced on the clock is applied to the transmittal
signals. Depending on the implementation, the variation is seen
either on the carrier phase (modified zero crossings) or the data
symbol falling edge (modulation of to the pulse duration). A
receiver using an HSO will see the modulation and will then
demodulate it.
[0017] One modulation method used is Gaussian Clock Dither
Modulation (GCDM). GCDM uses a combination of statistical
variation, spread spectrum and direct clock quantization. GCDM does
not require making the jitter any worse than that of a typical,
high quality, oscillator. Typical jitter in these oscillators is
approximately 1 s-1.0 s of picoseconds (ps). GCDM transmits "Marks"
and Spaces" using a Gaussian distributed random variable to
determine the amount of jitter to add to each symbol. Using a
Gaussian distributed random variable ensures that the jitter looks
Gaussian, as jitter is, and keeps the jitter to a deviation
commensurate with a well-designed communications system.
[0018] All communication systems have jitter. The greater the
stability of the system's reference oscillator, the less jitter in
the system. Timing jitter is illustrated in FIG. 1. Jitter is
defined as the undesired deviation from true periodicity of an
assumed periodic signal 10. As shown in FIG. 1, jitter causes the
falling edge 12 (or rising edge) of a pulse to jitter about a mean
value 13. The mean value is the desired periodicity.
[0019] For purposes of consistency of terminology, "accuracy" is
how close the pulse repetition rate is to a known standard, whereas
"precision" is describes the periodicity of the pulse train. The
concepts of accuracy and precision are illustrated in FIG. 2.
Synonyms used for precision are stability and uncertainty; these
two terms are used interchangeably throughout this paper. There is
however a subtle difference in the three terms. Precision is an
absolute measure such as plus or minus a deviation from the mean.
Uncertainty is more appropriate when discussing system performance
statistically. Stability is used when one wants to refer to the
affect that the precision has on the overall system
performance.
[0020] In any communication system, the zero crossings of the
electrical signals vary and are centered about a mean value, which
is the desired periodic interval. The jitter is a result of
oscillator instability and has both random and deterministic
components. The deterministic component is measureable and is
therefore not of concern for this discussion. The random jitter
component is Gaussian in nature; it is this property that is
exploited for the covert channel.
[0021] Some embodiments of the present invention use an HSO having
a sufficiently low jitter such that modulation may be added to that
inherent instability but still kept below the minimum levels of
detection and capture circuitry utilizing a standard reference
source.
[0022] FIG. 3 shows a graph of jitter 16 from a suitable
oscillator. Any suitable highly stable oscillator may be used. An
HSO has very low phase noise, with an equivalent timing jitter on
the order of femtoseconds (fs), even for very high reference
frequencies (GHz), Typical root mean squared (rms) jitter 18 is on
the order of 1 s-10 s of picoseconds.
[0023] FIG. 4 shows a block diagram 30 suitable for describing the
general operation of a system and method constructed according to
the present invention using FIG. 4 shows a block diagram 30
suitable for describing the general operation of a system and
method constructed according to the present invention using GCDM. A
host communication system 32 uses the output of HSO clock 34 as its
primary reference providing the system 32 with an rms timing jitter
of .about.10 s fs. Host system 32 likely introduces some further
jitter. Surreptitious communications of covert data 36 is then
affected by modulating the reference clock signal from HSO clock 34
with the covert data 36, in the HSO modulator. The resulting
modulated clock signal is then used for sending nominal data via
host data encoder 40 from host data source 42 over a communications
channel 44. Communications channel 44 can be terrestrial, such as
copper and fiber optic, or over-the-air.
[0024] On the receive side 46, a Host Data Decoder 48 recovers the
host data without any additional processing beyond that required
for the transmission type. Signals from communications channel 44
are also coupled to Demodulator 50, which recovers the covert data
by reference to an HSO clock 54. Although FIG. 5 shows an HSO clock
34, 54 at both ends of the communications system, it is possible to
design a system such that only one HSO is required on the receive
side 46.
[0025] FIG. 5 shows a representational graph of the timing
variations used in the covert communications channel. The trace 60
in the figure is the probability distribution of a typical
oscillator used in a communication system. A "Mark" or a "Space" is
transmitted by using a Gaussian random variable to modulate the
phase/frequency of the HSO. The location of the "Mark" and "Space"
is determined as follows: The full extent of the dither window is
divided into two regions. If one assumes for example that the full
extent is 20 ps, then the regions are, -10 to 0 and 0 to 10. A Mark
is then described by a Gaussian random variable with a mean 62 of
-5 ps and a standard deviation of 1 ps. Similarly, a "Space" is
described by a random variable with a mean 64 of +5 ps and a
standard deviation of 1 ps as shown in FIG. 5.
[0026] Statistically, there are times that the system's jitter will
obscure the signaling in the covert communications channel. To
mitigate this problem, the covert signal is spread using a Direct
Sequence Spread Spectrum (DSSS) technique. The DSSS signal is a
Maximal Length Sequence (TBR) of length 1025 chips (TBR) which
provides a process gain of 30 dB (TBR).
[0027] In the manner describe above, a method for carrying data on
a live host signal, comprises the steps of: varying timing in a
host signal in response to data to be encoded, wherein variations
in timing are smaller than a sampling period for detection and
capture of the digital signal; receiving the live host signal;
sensing timing variations in the received live host signal by
comparison to a reference signal; and determining information in
the sensed timing variations. The variations in timing may be less
than 1 picosecond. The host signal may be a digital signal and the
timing variations may be pulse timing variations. The variations in
pulse timing may include variation of a leading edge, a trailing
edge and pulse width of digital pulses and are smaller than the
sampling period for detecting and capturing the digital signal. The
reference signal may be a frequency reference having a stability
that is better than the level of timing variations of the host
signal. Although the method is discussed in terms of a digital
signal, the principals are also applicable to analog signals.
[0028] Following is a discussion of a system and method for
measuring variations or deviation from ideal waveform transitions
in a received signal to thereby access covert data encoded
according to the above described method.
[0029] FIG. 6A shows a plot of three digital waveforms 70, 72, 74.
Waveform 70 is an example of a digital waveform which has been
modulated by the method of the above described invention. Gray or
blurred areas 71 represent timing variation or jitter which may
occur in individual pulse transitions due to the modulation thereof
with covert data. The term pulse transitions refer to leading and
trailing edges of the pulses. Waveform 72 shows the same host
waveform as waveform 70, except without the timing jitter 71.
Waveform 74 shows an example of a reference signal useful for
decoding the covert data in waveform 70. FIG. 6B is a variation of
FIG. 6A showing a modulated host waveform 76 along with
reconstructed waveform 72, and reference waveform 74. Host waveform
76 shows two pulses 75, 77 having leading and trailing edges which
are aligned with the pulses of reference waveform 74. Waveform 76
further shows a center pulse having a leading edge 78 which is
advanced and a trailing edge 79 which is delayed which misalignment
represents data as depicted in the graph of FIG. 5.
[0030] FIG. 7 is a block diagram of a circuit constructed according
to the present invention. A processing circuit 80 receives the
incoming encoded waveform 70 of FIG. 6 along with the reference
clock signal 74. Processing circuit 80 reconstructs a copy 72a of
the incoming waveform 70 which copy does not induct the timing
variations or jitter of received waveform 70. This reconstructed
waveform 72a is substantially identical to waveform 72 of FIG. 6 in
that it replicates the nominal digital data present in host
waveform 70. Waveform 72a is reconstructed using the reference
signal 74 and thus has the stability of the original host signal
prior to the addition of the non-persistent channel. Both the
original host signal 70 and the reconstructed host signal 72a are
simultaneously coupled to phase detectors 82, 83 along with
identical copies of reference signal 74. Processing circuit 80
necessarily includes a slight delay for host signal 70 due to the
reconstruction process. This delay enables phase matching between
host signal 70 and reconstructed signal 72 a in their respective
phase detectors 82, 83. The outputs 84, 85 of phase detectors 82,
83 are coupled to a comparator 88 which subtracts one signal from
the other, resulting in a combined signal 90.
[0031] FIG. 8 is a graphic depiction 100 of the application of the
present invention to analog waveforms. A pair of phase detectors
102, 103 provide waveforms 104, 105 as a result of phase detecting
an analog host signal 98 against a reconstructed copy 99. Waveforms
104, 105 are shown as overlaid in the upper right portion of the
figure, and further shown as subtracted as they would represent the
output 106 of comparator 107 waveform. Waveform 105 is subtracted
by comparator 107 and is therefore inverted as waveform 105a in the
output signal 106. The resulting difference between waveforms 104
and 105 is shown as waveform 108. Portions of waveform 108
extending above zero line 109 could represent a logical "1" and
portions of waveform 108 extending below zero line 109 could
represent a logical "0".
[0032] The present application, METHOD AND SYSTEM FOR
NON-PERSISTENT COMMUNICATION is being filed on the same day as and
in conjunction with related applications: METHODS FOR ENCRYPTION
OBFUSCATION; SYSTEM AND METHOD TO DETECT TIME-DELAYS IN
NON-PERIODIC SIGNALS; and METHOD AND SYSTEM FOR NON-PERSISTENT
REAL-TIME ENCRYPTION KEY DISTRIBUTION, which applications all share
some common inventors herewith, and the contents of which are all
hereby incorporated herein in their entirety.
[0033] The present invention is illustratively described above in
reference to the disclosed embodiments. Various modifications and
changes may be made to the disclosed embodiments by persons skilled
in the art without departing from the scope of the present
invention as defined in the appended claims.
* * * * *